**This animation** is based on a section of the (*forthcoming*) book,
* SPECIAL RELATIVITY ILLUSTRATED,* by John de Pillis.

**A Frame of Reference** can be regarded as a ruler with identical clocks (indicated by the red boxes)
at each and every point. An observer standing at point x reading time t at his/her
specific clock is indicated by the ordered pair, [x,t]. These are the
spacetime coordinates of the observer.

**In relativistic physics,** time is not universal.
Even though all clocks at rest are identical and two observers at x=0 may
synchronize their watches at time t=0, their clock readings will diverge
(un-synchronize) if the observers are in motion relative to each other.

**In this animation,** two observers on separate frames are traveling at
speed 0.6*c* relative to each other. If we stand on one frame and
observe the moving frame, then we see the moving clocks running at 80%
the rate of our own (stationary) clocks. Moreover, we perceive lengths of
rulers that move in the direction of motion to contract to 80% the
lengths of identical stationary rulers.